It’s easy to see why the celebrities or power players are on the list—no one has to be convinced that Barack Obama or Mitt Romney are two of the most influential people on the planet. But there are always more obscure people on the list, often scientists or those in business, who can make waves even though they’re not household names. For last year’s TIME 100 I wrote about Nathan Wolfe, the cutting-edge virologist who is working to head off new pandemics before they begin—and then profiled him in full later that year. And this year I want to highlight four TIME 100 honorees in science and energy who may not be famous, but whose work is changing the world: tight oil tycoon Harold Hamm, Brazilian oil CEO Maria des Gracas Foster, chemist Donald Sadoway and virologist Ron Fouchier.

We can start with Hamm. Last month I wrote a cover story for TIME on the future of oil—and part of that future is being written in North Dakota, where a mini crude boom is underway. The crude found in the Peace Garden state is tight oil, unlocked by fracking, and the man most responsible for the millions of gallons of new oil is Harold Hamm. Hamm is the CEO of Continental Resources, an Oklahoma-based oil company, and he’s been driving the tight oil story from the beginning, as this profile in Bloomberg Businessweek shows. The title is appropriate: “The Man Who Bought North Dakota“:

Today, Continental, with a stock market value of $13.5 billion, vies with oil giants such as Hess (HES) for the most Bakken acres under lease (more than 900,000), the most drilling rigs (24), and the most wells (more than 350). Continental’s revenue has nearly tripled from two years ago to an expected $1.76 billion in 2011, while profits have grown sevenfold to an estimated $538 million, according to data compiled by Bloomberg. Hamm and his family control 78 percent of the company’s shares, a stake valued at more than $10 billion.

Hamm, a stocky man of medium height with a leprechaun’s playful grin and a diamond-studded Continental ring on his right hand, has revived a character who had faded from the American oil patch. He’s a wildcatter, the sort of oil hunter unafraid to lease land and put a drill bit in the ground where there might or might not be crude. “I find oil,” he says as he drives to the company jet that will take him back to Continental headquarters in his native Oklahoma. “In America, people lost the will to drill for oil. But I’m a little more hardheaded than other people.”

Hamm is on the TIME 100 list because of that hardheaded attitude, that wildcat sprit that has marked the U.S. oil industry. The boom in shale gas and shale oil is changing the energy picture in the U.S., and it’s due to the efforts of risktakers like Hamm (along with a little help from the government). The environmental consequences of the shale boom are still being reckoned, but Hamm’s influence is undeniable.

Maria das Gracas Foster is another oil baron, but a very different one. Foster is the new CEO of the Brazilian oil giant Petrobras, responsible for overseeing that company’s $225 billion effort to drill for billions of barrels of offshore oil. (I wrote about visiting a Petrobras oil platform back in January.) Foster is the first woman in charge of a major international oil company, and a rare female leader in macho Brazil. A child of the favelas of Rio—where she sold paper and other recyclables to help pay for school—Foster has worked with Petrobras nearly her entire career, but now she’s the one who will have to take the company to the next level. Her success or failure will have major ramifications for Petrobras—and for Brazil.

Donald Sadoway might be the least well known person on the TIME 100 list, but his work might be the most important. Sadoway, a chemist at the Massachusetts Institute of Technology, is working on advanced battery technology that could prove to be a game changer for renewable energy. Wind and solar will always be hobbled by the fact that the power they generate is intermittent, and current batteries are far too expensive to store that power for later. But Sadoway think he’s created a battery that will change all of that by… well, I’ll let him explain:

Ron Fouchier doesn’t work in the energy or environment fields—but then again, there was a time when I didn’t either. When I worked in Hong Kong, from 2001 to 2006, I spent more time than I’d like to remember covering avian influenza. I saw the H5N1 flu virus jump from sick birds to human beings, killing nearly all it infected and triggering fears of a full-blown global pandemic of the sort not seen since 1918.

That didn’t happen—or at least, it hasn’t happened yet—because the H5N1 virus hasn’t mutated the ability to both kill humans easily, which it already does, and spread easily from person to person, which it doesn’t yet do. But Fouchier, a Dutch virologist at Erasmus University, has developed a man-made H5N1 virus that appears to combine the best—or the worst—of both worlds. Fouchier says he developed his artificial super-flu to better understand the H5N1 virus, and prepare for the next inevitable pandemic—but his research has touched off a firestorm in the media and among scientists. The full results of Fouchier’s research still haven’t been published because some believe the work is simply too dangerous. Whether or not his research is ever made public, Fouchier has already earned a place in scientific history for forcing us to come to grips with our ability to manufacture custom microbes in the lab—whether or not we should. That’s real influence.